Method and apparatus for transferring electrical power

ABSTRACT

A method and an apparatus for transferring electric power to an electrical load ( 105 ); the method includes steps of: converting a direct electric current into an electric tension wave, applying the electric tension wave in inlet to at least a couple of electric capacitors ( 125, 130 ); supplying the electrical load ( 105 ) with the electric tension in outlet from the capacitors ( 125, 130 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.14/389,507, filed Sep. 30, 2014, which is a 371 U.S. National Phase ofPCT/IB2013/000464 filed Mar. 19, 2013, which are incorporated byreference as if fully set forth.

FIELD OF THE INVENTION

The present invention relates in general to a method and an apparatusfor transferring electrical power to an electrical load. The electricalload can be for example any electrical or electronic device which has tobe electrically powered in order for it to function and/or to charge theinternal batteries of the device. Classic examples of this type ofelectric/electronic device are cellular telephones, computers,televisions and the like.

BACKGROUND

A solution that is at present very widely used for transferring electricpower to a charging device is that of using an AC/DC converter able toconvert an alternating current (AC), generated for example by a commonelectric grid, into a direct current (DC) suitable for supplying thecharging device.

To realize an AC/DC converter capable of transferring high electricpower to the charging device, with high performance, low encumbrance andlow costs, a circuit is generally used having some typicalcharacteristics.

The circuit comprises, firstly, a high-tension rectifier, normally adiode bridge rectifier having possibly a tension and/or currentstabilization circuit, which is connectable to the electrical grid,normally by means of an electric plug, such as to convert alternatingcurrent supplied by the electrical grid into a direct current. The hightension continues in output from the rectifier thus applied to a DC/DCconverter suitable for modifying the direct current in order to make itsuitable for supplying the charging device.

The DC/DC converter normally comprises a HF (high frequency) source,able to generate waves of high-tension electric tension (at present ofthe order of tenths or hundredths of kHz), according to circuit types ofthe flyback type, or the like. The tension waves are then sent to an HFtransformer which galvanically isolates the high-tension primary circuit(rectifier and generator of tension waves) from the low-tensionsecondary circuit which comprises the charging device. This galvanicisolation is necessary to prevent damage or overtensions in the primarycircuit from endangering the second circuit, which is low-tension andnormally located close to the user (for example the exposed contacts ofthe connectors of a cell-phone or a computer).

To regulate the direct tension of the secondary circuit, it is usual tointervene on the duty-cycle of the high-frequency waves generated by theactive switch.

The secondary circuit generally comprises a second rectifier (forexample a single bridge rectifier or a double diode bridge rectifiercombined with a center-tap transformer, a synchronous rectifier, etc.),electrically interposed between the transformer and the charging device,which is suitable for converting the low-tension waves exiting from thesecond circuit of the transformer into a direct low tension. A filtercan be interposed between the rectifier and the charging device, forstabilizing the tension and/or the current on the charging device.

A well-established need in this sector is that of reducing thedimensions of DC/DC converters as much as possible. To attain thisobjective, given an equal power to apply to the charging device, it isfundamental to increase the frequency of the tension waves generated bythe HF source, as in this way, over the time unit, the number of cyclesin which electrical energy is transferred from the primary circuit tothe second circuit is increased, thus also increasing the transferredpower.

Increasing the frequency of the tension waves leads tendentially to thedrawback of increasing the leakages in the ferromagnetic material whichrealizes the magnetic circuit of the transformer and the dynamic leakagein the active switch during the switching on and off of the activeswitch, which sets a limit to the maximum frequency of the tension waveswhich can be generated by the HF source and thus to minimum dimension ofthe transformer and the heat removing elements of the heat dissipated inthe converter.

SUMMARY

In the light of the above, an aim of the present invention is to makeavailable a method and an apparatus for transferring electrical power toa charging device, which effectively enables, at the same time,minimizing the problem of leakage, typical of DC/DC converters availableat present.

A further aim of the invention is to guarantee effective galvanicisolation between the primary circuit and the secondary circuit at thesame time.

These and other aims besides are attained by the characteristics of thevarious embodiments of the invention reported in the independent claims.The dependent claims delineate preferred and/or particularlyadvantageous aspect of the various embodiments of the invention.

An embodiment of the invention discloses a method for transferringelectrical power to an electrical load, comprising steps of:

converting an direct electric current into an electric tension wave,

applying the electric tension wave in inlet to at least a couple ofelectric capacitors,

supplying the electrical load with the electric tension in outlet fromthe capacitors.

In other words, this embodiment substantially comprises replacing thetransformer of the prior art with at least two electrical capacitors,thus solving the problem of leakage in the transformer.

The presence of this pair of capacitors is further able to guaranteegalvanic isolation between the primary circuit and the secondarycircuit, as well as transferring an electrical power sufficient tosupply the charging device.

Each capacitor supplied with a tension wave can be considered animpedance, such that by means of a frequency of the tension wave that issufficiently high and/or by means of electrical capacitors that aresufficiently large and/or by means of a tension wave having asufficiently large amplitude, it is advantageously possible to obtain,in outlet from the pair of electrical capacitors, a tension wave that issufficiently large for supplying the charging device.

In an aspect of the invention, the method can also comprise a step of:

rectifying the electric tension wave in outlet from the electricalcapacitors.

This embodiment of the invention is advantageous when the chargingdevice must be supplied with a direct electrical current.

In a further aspect of the present invention, the step of converting thedirect electric tension into a wave of electric tension can comprise:

alternatingly switching an active switch, for example a transistor(MOSFET, BJT, IGBT, etc.) on and off.

In other words, this aspect of the invention introduces the possibilityof generating the tension wave by means of a switching action, whichrepresents a very simple solution that is reliable and easilycontrollable.

In this context, it is worthwhile to consider that transmitting highpowers via the electrical capacitors with a switching action is not asimple, ordinary undertaking. Increasing the amplitude of the tensionwave by a considerable amount typically means using a transformer or astep-up circuit before the galavanic isolation capacitors and atransformer or a step-down circuit after the galavanic isolationcapacitors, with a relative increase in encumbrances, leakage and costs.

Increasing the amplitude of the tension wave is further deleterious interms of safety. On the other hand, increasing the capacitors meansusing dielectric materials with higher dielectric constant and/orreducing the thickness of the dielectric, with a relative worsening ofthe galvanic isolation and an increase in electric leakage and/orincreasing the dimensions of the armatures, with a consequent increasein the encumbrances.

Lastly, increasing the frequency of the tension wave with some switchingsystems of known type, such as for example bridge or half-bridgeswitching layouts, possibly resonant or almost resonant, generally leadsto an increase in leakages and a difficult and expensive driving of theactive switches, due to the presence of switches referring to a floatingnode.

For this reason, an aspect of the invention comprises that the step ofconverting the direct electric tension into a wave of electric tensioncan include the step of:

lowering the electrical power (tension and/or current) applied to theactive switch to a substantially nil value during each transition stepof the active switch: both from off (inhibited) to on (saturation), andfrom on to off.

In this way the electric leakages are considerably reduced during theswitching cycles, in this way enabling an increase in the frequency ofthe cycles and thus the frequency of the tension wave generated thereby,with the result of being able to increase the electrical powertransmitted given a same applied tension, or being able to lower thetension applied given a same transmitted electric power.

In a further aspect of the invention the step of conversion of thedirect electrical tension into a wave of electrical tension can includeusing a circuital scheme based on a single active switch referred to afixed potential, i.e. alternatively switching on and off, following theabove-described modes, a single active switch, for example a singletransistor (e.g. MOSFET, BJT, IGBT, etc.).

In this way, as well as the above-described advantages, the circuitcomplexity is much-reduced and the driver of the active switch issimplified, which can therefore be piloted at higher frequencies.

On the other hand, a typical problem which might arise when applyingthis method is the difficulty of controlling the power transferred tothe charging device, due to the fact that this transferred power mightdepend on the charging device itself, which in turn might be neitherconstant nor known a priori.

Typically, in fact, resonant layouts with only one transistor areapplicable to constant and known loads, as each displacement of the workpoint from the design point determines a drop in performance or a faultybehavior of the system.

For this reason, other aspects of the invention relate to the modes withwhich it is possible to vary the power transmitted to the electriccharging device.

According to one of these aspects, the method can comprise the step of:

preventing or altering one or more cycles of on-and-off switching of theactive switch.

When the switching-on and off cycles are inhibited, i.e. not performed,the electric power overall transmitted to the charging device isadvantageously reduced, highly-efficient and with very low electricleakages.

The switching-on and off cycles can be inhibited for example bytemporarily suspending the electric piloting signal of the activeswitch.

In more detail, an aspect of the invention includes the possibility ofregulating the number and/or frequency of the cycles that are inhibited,on the basis of a predetermined reference value of the electric powerwhich is to be transferred to the charging device.

In this way it is advantageously possible to regulate the electric powertransmitted to the charging device such as to attain the above-mentionedreference value, which can be modified according to the specificcharging device to be supplied and more in general according to needs.

Still more in detail, the regulating of the electrical power transferredcan be performed with a feedback control which comprises for examplesteps of:

measuring the electrical power transferred to the charging device,

calculating the difference between the electrical power measured and thepredetermined reference value, and

regulating the number and/or the frequency of the switching on and offcycles inhibited, such as to minimize the difference.

In addition to, or alternatively to the first mode of regulation of theelectrical power to the charging device, a second mode of regulation canbe used, which comprises the step of:

temporarily deviating the electric tension wave onto an electrical lineset in parallel to the electrical load.

When the tension wave is deviated on the electric line, the chargingdevice is not supplied, such that the electric power transmitted theretois overall reduced.

In order to enable this deviating step, the electric line can comprise asecond active switch, for example a second transistor (MOSFET, BJT,IGBT, etc.), and a third capacitor connected in series with the secondactive switch and having a capacitor value that is sufficiently high tobe considered a short-circuit with respect to the charging device, whenthe second active switch is switched on (i.e. in saturation).

In this case too, an aspect of the invention includes regulating theduration of the switching step and/or the frequency with which thedeviating step is eventually repeated, on the basis of a predeterminedreference value of the electric power which is to be transferred to thecharging device.

In this way it is advantageously possible to regulate the electric powerreally transmitted to the charging device in such a way as to attain thereference value, which can be modified according to the specificcharging device to be supplied.

In particular, the regulating of the electrical power transferred can beperformed with a feedback control comprising for example steps of:

measuring the electrical power transferred to the charging device,

calculating the difference between the measured electrical power and thepredetermined reference value, and

regulating the duration of the deviation step and/or the frequency withwhich the deviation step is eventually repeated, such as to minimize thedifference.

A third strategy for regulating the electrical power to the chargingdevice can comprise the step of:

regulating the initial direct electric tension.

The regulating of the initial direct electric tension is obtainable forexample by means of a DC/DC converter of any type, for example linear,switching and others besides.

As in the preceding cases, this strategy too can comprise regulating theelectric tension on the basis of a predetermined reference value of theelectrical power which it is desired to transfer to the charging device,for example by means of a feedback control of the electric poweractually transferred.

This third strategy can be implemented alternatively or in combinationwith one or more of the preceding strategies.

A different aspect of the invention relates to the generating of theinitial direct tension.

This direct tension can in fact be generated via a direct tensiongenerator, for example a battery, or can be generated by the step ofrectifying an alternated electric tension, which is provided for exampleby a common electric distribution grid.

In a different aspect of the invention, a first armature of each of thecapacitors is installed on a user device, while the second armature ofeach of the electrical capacitors is installed on a supply deviceseparate and independent of the user device, and the method comprisesnearing the user device to the supply device such that the armaturesinstalled on each thereof realize a same galvanic isolation capacitor.

This aspect of the invention delineates a method for transferringelectrical power in a capacitive way, wireless, between the supplydevice and the user device, which can thus be electrically supplied inorder to function or for charging the internal batteries thereof.

In this way it is possible to supply an electrical/electronic device,such as for example a cell-phone, simply by resting the device on thesupply device, without galvanic contacts, such that the armaturesinstalled in one and the other realize the capacitors described hereinabove.

A further embodiment of the invention discloses an apparatus fortransferring electrical power to an electrical load, comprising:

at least a pair of electric capacitors,

means for converting a direct electric tension into an electric tensionwave,

means for applying the electric tension wave in inlet to the capacitors,

means for supplying the electrical load with the electric tension inoutlet from the capacitors.

This embodiment of the invention essentially provides an apparatus whichenables performing the transfer method of the electrical power describedherein above, thus obtaining the relative advantages.

In particular, the presence of the two capacitors is able to guaranteegalvanic isolation between the primary circuit and the secondarycircuit, as well as transferring an electrical power that is sufficientto supply the charging device, at the same time resolving the problem ofthe electric leakages of the transformer and in the active and reactiveelements that are used in the prior art.

In an aspect of the invention, the apparatus can also comprise:

means for rectifying the electric tension wave in outlet from thecapacitors.

This embodiment of the invention is advantageous when the chargingdevice is to be supplied with a direct electric tension.

In a further aspect of the invention, the means for converting directelectric tension into an electric tension wave can comprise a switchingcircuit provided at least with:

an active switch, for example a transistor (MOSFET, BJT, IGBT, etc.),and

means (driver) for generating an electrical pilot signal suitable forswitching the active switch on (i.e. saturation) and off (i.e.inhibition) alternatingly.

In more detail, switching circuits can be used that make use of one onlyactive switch, for example one transistor alone (MOSFET, BJT, IGBT,etc.), relating preferably to a fixed, preferably minimum and lowpotential (ground), which represents a very simple solution, reliable,easily controllable and economical. Alternatively, other types ofswitching circuits can be used, which comprise, for example, two or moreactive switches, with the relative drivers.

It is further specified that the switching circuit (i.e. the electricalcomponents making it up) might be physically located either upstream ofthe galvanic isolation capacitors or downstream thereof, i.e. betweenthe galvanic isolation capacitors and the charging device, as the onlything that counts is that electric tension waves be applied to thecapacitors.

In this context too, it is worthwhile mentioning that not all knownswitching circuits are able to generate a high-power tension wave with amodest degree of leakage.

For example, some typical switching circuits make use of floatingtransistors, which therefore require drivers provided withintrinsically-slow bootstrap circuits, or hard-switching circuits withhigh levels of dynamic leakage, which in fact limit the maximumswitching frequency and therefore the frequency of the tension wavegenerated.

For this reason, in a preferred aspect of the invention, the convertingmeans of the direct electric tension into the electric tension wave alsocomprise a reactive circuit, for example almost resonating orresonating, which is regulated such as to lower the electric power(tension and/or current) dissipated by the active switch of theswitching circuit to a substantially nil value, during each transitionstep of the active switch: both from off to on and from on to off.

A reactive circuit is an electric circuit comprising one or morecondensers and one or more inductors specially connected to one another.The setting-up of the reactive circuit consists in dimensioning thecondensers and inductors, in terms respectively of capacity andelectrical inductance.

In this aspect of the invention, the converting means of the directelectric tension into the electric tension wave comprise in practice acircuit diagram which, considering both the switching circuit and thereactive circuit, is assimilable to the circuit of an amplifier of classe, f, e/f or the like.

In this way the electrical leakages during the switching cycles of theactive switch are considerably quashed, enabling in this way an increaseto be made in the frequency of these cycles and therefore the tensionwave frequency generated thereby, with the result that the electricpower transmitted can be increased given a same applied tension, or theapplied tension can be lowered given a same transmitted electric power.

Increasing the frequency of the electric tension brings the advantage ofbeing able to reduce the dimensions of all the reactive components, andin particular the galvanic isolation capacitors, given a same electricpower to be transmitted.

In an aspect of the invention, the reactive circuit can be set up insuch a way as to filter the electric tension wave, leaving at least oneof the fundamental frequencies thereof to pass towards the electricalcharging device.

Considering the case of piloting the active switch of the switchingcircuit with a square-wave electric signal having a duty-cycle of 50%,the reactive circuit can be set up such as to allow the firstfundamental frequency of the electric tension generated to pass, inwhich case the generating means of the tension wave will be assimilableto an e-class amplifier. Alternatively, the reactive circuit can be setup such as to allow the third fundamental frequency and/or other greaterharmonics of the electric tension wave to pass, in which case thegenerating means of the tension wave will be assimilable to an f-classamplifier. It is however possible for the reactive circuit to be set upin such a way as to allow fundamental frequencies of higher frequenciesto pass, or to allow several frequencies to pass at the same time, witha similar behavior to an e/f class amplifier or the like.

This aspect of the invention has the advantage of improving the transferof electrical power to the charging device and of minimizing the energydissipated.

It is specified at this point that the electrical components definingthe reactive circuit might be physically located all upstream of thegalvanic isolation capacitor, or all downstream thereof, or between thegalvanic isolation capacitors and the charging device, or they might bedistributed in part upstream and in part downstream of the galvanicisolation capacitors, without this modifying the effect.

Further, the galvanic isolation capacitors might even be an integralpart of the reactive circuit, or might be independent thereof.

Further aspects of the invention relates to the way in which the powertransmitted to the electrical charging device can be varied.

In one of these aspects, the apparatus can comprise means forcontrolling the electrical pilot signal, the control means beingconfigured for:

-   -   suspending or modifying the generating of the electrical pilot        signal, such as to prevent or alter one or more consecutive        switching on and off cycles of the active switch.

During the inhibited cycles the electrical load is not supplied and thesystem continues to oscillate according to free damped oscillationmodes. During the cycles effected, the charging device is insteadsupplied and the system oscillates according to forced oscillatingmodes.

As explained in the foregoing, this aspect of the invention has theadvantage of enabling a variation in the overall electric powertransmitted to the charging device, with very small electric leakage andhigh efficiency.

In more detail, an aspect of the invention comprises the possibilitythat the control means are configured to regulate the number and/orfrequency of the cycles which are inhibited (i.e. the duration of thesuspension of the pilot signal and/or the frequency with which thesuspension can possibly be repeated), on the basis of a predeterminedreference value of an electrical parameter that is characteristic of theelectric power to be transferred to the load.

The above electrical parameter that is characteristic of the electricpower can be the electric power itself, or can be the supply tension ofthe charging device or possibly the supply current transmitted to thecharging device.

In this way it is advantageously possible to regulate the electricparameter characteristic of the electric power transmitted to thecharging device in such a way as to attain the above-mentioned referencevalue, which can be modified according to the specific charging deviceto be supplied.

Still more in detail, the control means can be configured such as:

measuring, using appropriate sensors, the above-mentioned electricparameter characteristic of the electric power, for example by means ofa sensor suitable for generating a feedback signal coming from thesecondary at low tension, or using sensors suitable for measuring one ormore tension and/or current values on the primary from which the poweron the charging device can be indirectly calculated, then

calculating the difference between the measurement of the electricalparameter characteristic of the electric power and the predeterminedreference value, and

regulating the number and/or the frequency of switching-on and offcycles which are inhibited, such as to minimize the difference.

In addition or alternatively to the control means, the apparatus cancomprise:

means for temporarily deviating the electric tension wave onto anelectrical line set in parallel to the electrical load.

When the tension wave is deviated onto the electric line, the chargingdevice is not supplied, such that the electric power transmitted theretois overall reduced.

The means for deviating the electric tension wave can comprise forexample a second active switch, for example a transistor, a thirdelectric capacitor arranged in series to the second active switch alongthe electric line, and means (driver) for generating an electrical pilotsignal for switching on (i.e. saturation) and off (i.e. inhibiting) thesecond active switch, alternatingly.

The third electric capacitor must have a sufficiently high value to beconsidered as a short circuit with respect to the charging device, whenthe second active switch is on (i.e. in saturation).

In this way, when the second active switch is on, the electric energytransferred by the capacitors is deviated onto the control capacity,while when it is off the charging device absorbs all the energy.

It is notable that the efficiency of the system can be constantly high,as when the second active switch is on, there is only reactive powerexchanged in the circuit, while when it is off, the energy istransferred to the charging device.

The electric pilot signal of the second active switch can be a PWMsignal or the like, such that the electric power transmitted to thecharging device is proportional to the duty-cycle of the electric pilotsignal.

Note that the pilot signal of the second active switch is independentfrom the pilot signal of the active switch of the switching circuit.

An aspect of the invention includes the possibility that the apparatuscomprises means for regulating the duration of the deviation step and/orthe frequency with which the deviation step is eventually repeated, onthe basis of a predetermined reference value of an electric parametercharacteristic of the electric power that is to be transferred to thecharging device.

In this case too, the electric parameter characteristic of the electricpower can be the electric power itself, or can be the tension of thesupply charge or even the supply current transmitted to the chargingdevice.

In this way it is advantageously possible to regulate the electricparameter characteristic of the electric power transmitted to thecharging device in such a way as to attain the reference value, whichcan be modified according to the specific charging device to besupplied.

The regulating means can comprise for example a control circuitconfigured such as to regulate the duty-cycle of the electric pilotsignal of the second active switch mentioned in the foregoing.

In more detail, the control circuit can be configured for:

measuring the above-mentioned electric parameter characteristic of theelectric power,

calculating the difference between the measurement of the electricparameter characteristic of the electric power and the predeterminedreference value, and

regulating the duty-cycle of the electric pilot signal of the secondactive switch, such as to minimize the difference.

Note that this regulating system is very reactive and that the ripple onthe output tension can be very small. In fact, considering that theworking frequency of the tension-wave generating circuit (e.g. class eor f or elf) is very high, the control circuit can work at any frequencyindependently of the working frequency of the tension-wave generatingcircuit, and therefore if necessary also at high frequencies (even MHzor hundreds of kHz), thus with very small ripples.

A further advantage of this functioning diagram is the totalindependence of the control circuit, located on the secondary, withrespect to the primary circuit.

This enables eliminating a further expensive transmission circuit of thefeedback signal from the primary to the secondary (typically anopto-isolator or another transferring means of the primary or secondaryfeedback signal in any case guaranteeing galvanic isolation), as thewhole control process occurs on the side of the low-tension circuitside.

Again, for regulating the electric power transmitted to the load, theapparatus can comprise, additionally to or alternatively to theabove-described means, means for regulating the initial direct electrictension.

The regulating means can comprise, for example, a DC/DC converterlocated upstream of the switching circuit, for example a linear,switching or any other type of DC/DC converter.

As in the preceding cases, this aspect of the invention can alsocomprise the electric tension regulating means being configured in sucha way as to regulate the electric tension on the basis of an electricparameter characteristic of the electric power to be transferred to theelectrical load (the electric power itself, supply tension of thecharging device or supply current of the charging device), for exampleby means of a feedback control diagram.

A different aspect of the invention relates to the generating of theinitial direct tension.

In an aspect of the invention, the apparatus can comprise a directtension generator, for example a battery, for supplying the convertingmeans which generate the electric tension wave.

In this case, the whole apparatus would in fact fall within the categoryof DC/DC converters.

Alternatively, the apparatus can comprise rectifier means, for example adiode bridge rectifier with a filter for reducing the output ripple,which are connectable to an alternating tension source, for example acommon electric distribution grid, such as to rectify the alternatingelectric tension into a direct electric tension and supplying the directelectric tension to the converter means for generating the electrictension wave.

In the second case, the whole apparatus falls in fact into the categoryof AC/DC converters.

In an embodiment of the invention, each of the galvanic isolatingcapacitors can be a pre-assembled component, i.e. a condenser, and thecapacitors can therefore be installed in a same device.

This embodiment is such that the whole apparatus constitutes in fact aconverter (taken to mean a single component), which can be connected viaelectric cables to an electrical load, such as for example anelectric/electronic device, which must be supplied or recharged.

Alternatively, in a further embodiment of the invention the apparatuscomprises a user device and a supply device, separate and independentfrom the user device, in which the user device comprises a firstarmature of each of the galvanic isolation capacitors, while the supplydevice comprises the second armature of each of the capacitors.

In this embodiment of the invention, the apparatus becomes suitable fortransferring electric power in a capacitive way and wirelessly betweenthe supply device and the user device, which is electrically suppliedsuch as to be able to function or for charging the internal batteriesthereof.

In particular, the user device can be any electric/electronic device,such as for example a cell-phone, a computer or the like, which can besupplied or recharged simply by resting on the supply device, such thatthe armatures installed in the receiving device and in the emittingdevice realize in fact the galvanic isolating capacitors describedherein above.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will emerge froma reading of the following description, provided by way of non-limitingexample, with the aid of the figures illustrated in the accompanyingtables of drawings.

FIG. 1 is a simplified circuit diagram of an apparatus for transferringelectric power according to an embodiment of the present invention.

FIG. 2 is a variant of the simplified circuit diagram of FIG. 1.

FIG. 3 is a more detailed circuit diagram of the apparatus of FIG. 1.

FIG. 4 is a variant of the circuit diagram of FIG. 3.

FIG. 5 is a variant of the circuit diagram of FIG. 4.

FIG. 6 schematically illustrates a practical realisation of theapparatus of FIG. 1.

FIG. 7 is a schematic diagram of a second practical embodiment of theapparatus of FIG. 1.

FIG. 8 is the detail VIII of FIG. 7, in enlarged scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, an embodiment of the present invention provides anapparatus 100 for transferring electrical power to an electricalcharging device 105.

The electrical charging device 105 may be for example any electric orelectronic device that must be powered to enable operation and/or tocharge the internal batteries of the device itself. Classic examples ofthis type of electrical/electronic device are mobile phones, computers,televisions and others besides.

From a circuit point of view, the apparatus 100 shown in the example ofFIG. 1 is a DC/DC converter, which is suitable for transferring electricpower from a DC tension source 110 to a charging device 105, which ishere generally denoted by an electrical resistance symbol.

The DC tension source 110 may be for example a battery.

Alternatively, the source 110 could include a rectifier 111, forexample, a diode bridge, a single diode, a coupled double diode, oranother synchronous rectifier, which is suitable for connecting with asource of alternating tension 112, for example a common electricaldistribution grid at 230V and 50 Hz, so as to rectify the alternatingtension generated by the source 112. A filter stabilizer may be presentimmediately downstream of the rectifier 111. In the second case, theapparatus 100 would be more properly configured as an AC/DC converter.

The apparatus 100 schematically comprises a primary circuit 115 directlyconnected with the source 110, and a secondary circuit 120 directlyconnected with the charging device 105, which are mutually electricallyisolated by at least a pair of isolating electric capacitors, of which afirst capacitor 125 and a second capacitor 130.

The primary circuit 115 comprises a converter 135 for converting thedirect electric tension generated by the source 110 into a tension wave,i.e. into a succession of tension pulses in which each tension pulsevaries from a minimum value, for example but not necessarilysubstantially nil, to a maximum value depending on the entity of the DCtension at input.

The tension wave in output from the converter 135 is then applied to thepair of capacitors 125 and 130, which transmit the tension wave to thesecondary circuit 120.

The secondary circuit 120 includes a rectifier 140, which is suitablefor rectifying the tension wave in output from the pair of capacitors,so as to newly obtain a DC tension. The rectifier 140 may be a bridgediode rectifier, a single diode, a coupled double diode, or anothersynchronous rectifier. Possibly, the rectifier 140 may be combined witha subsequent stabilization stage of the tension (e.g. LC filter orother).

The direct tension output from the rectifier 140 is then applied to theinput terminals of the electrical charging device 105 to be supplied.

In practice, the electrical charging device 105 is connected in seriesbetween the two capacitors 125 and 130 which, as they can be regarded asa pair of impedances, enable transmission to the secondary circuit 120of a sufficiently high tension wave to be rectified in the rectifier140, possibly stabilized, and then used to supply the charging device105.

Note at this point that in other embodiments the rectifier 140 may beabsent, thus obtaining a DC/AC (or AC/AC) converter capable of supplyingthe charging device 105 with an alternating tension.

Entering into more detail, in a preferred aspect of the invention theconverter 135 includes a switching circuit 142, which is suitable forgenerating the tension wave applied to the capacitors 125 and 130.

In general, the switching circuit 142 comprises at least one activeswitch 155, for example a transistor (e.g. BJT bipolar junctiontransistor, FET field effect transistor, MOSFET, MESFET, JFET, IGBT andothers besides), and a driver for applying an electrical pilot signal tothe active switch 155, which signal can turn on (i.e. in saturation) andoff (inhibit) the active switch.

Here it is specified that although in the present example the switchingcircuit 142 is located upstream of the galvanic isolation capacitors 125and 130, in other embodiments the same switching circuit 142 could beplaced between the galvanic isolation capacitors 125 and 130 and thecharging device 105, since the only thing that matters is that tensionwaves are applied to the capacitors 125 and 130.

In order to generate a wave of high frequency tension with lowelectrical leakages, the converter 135 may also include a reactivecircuit 145, for example, an almost-resonant, resonant or fully resonantcircuit, which is set up such as to lower the electrical power (e.g.tension and/or current) applied to the active switch 155 of theswitching circuit 142 to a value of substantially nil, during eachtransition of the active switch 155 from off to on and vice versa. Inaddition to the value of the electrical power, the reactive circuit 145is preferably set up so that the time derivative of the electric powerapplied to the active switch 155 is also substantially nil, during eachtransition of the active switch 155 from on to off and possibly viceversa.

It is specified here that, although the reactive circuit 145 of thisexample is located upstream of the galvanic isolation capacitors 125 and130, it could alternatively also be placed between the galvanicisolation capacitor 125 and 130 and the charging device 105, or some ofits components can be located upstream and others downstream of thegalvanic isolation capacitors 125 and 130, without thereby modifying theeffect.

Further, the galvanic isolation capacitors 125 and 130 may be anintegral part of the reactive circuit 145, or may be independentthereof.

Purely by way of example, the converter 135 can overall present thecircuit diagram shown in greater detail in FIG. 3.

The converter 135 of the example of FIG. 3 comprises a first inductor150, commonly called the choke or feed inductor, connected in serieswith the DC tension source 110. During normal operation, the firstinductor 150 behaves essentially as a direct current generator.

In series with the inductor 150, the converter 135 includes theabove-mentioned active switch 155, for example a transistor (MOSFET,IGBT, BJT or other), having a head (e.g. the drain of a MOSFET type N)connected with the output terminal of the inductor 150, and the otherend (e.g. the source for a MOSFET N-type) connected in circuit with thesource 110, and the piloting head (e.g. the gate for a MOSFET) connectedwith a driver 160, i.e. with an electrical/electronic device suitablefor generating and applying an active electric pilot signal to the pilothead of the switch 155.

The pilot signal can for example be a square wave electrical signal witha duty-cycle of 50%.

When the driving signal is ON (for example, a gate tension higher thanthe source for an N type MOSFET), the active switch 155 switches on(i.e. goes into saturation allowing passage of current in the activeswitch); when instead the drive signal is OFF (such as a lower gatetension than the source for a MOSFET), the active switch 155 is switchedoff (or is inhibited preventing the passage of current in the activeswitch).

In series with the inductor 150, but in parallel with the active switch155, the converter 135 can include a capacitor 165, the output terminalof which is connected in short circuit with the tension source 110, viaan electrical branch to which a head of the active switch 155 and thesecond isolation capacitor 130 are also connected.

In series with the inductor 150, but in parallel with both the activeswitch 155 and the capacitor 165, the converter 135 can comprise afurther inductor 170, which is connected in series with the firstisolation capacitor 125.

The inductor 170 can also be divided into two or more inductors thetotal value of which remains the same, placed upstream or downstream ofcapacitor 125 and 130, without the system changing the operatingprinciple.

In this way, when the active switch 155 is switched on, the inductor 150charges.

Instead, when the active switch 155 is switched off, the current flowsonly to the charging device, discharging the inductor 150.

Since the active switch 155 is switched on and off alternatingly byfollowing the pilot signal, success tension impulses are applied to theisolating capacitors 125 and 130 which overall form the above-mentionedtension wave, which is then transferred to the secondary circuit 120,and then applied to the charging device 105.

It is observed that in this embodiment the isolation capacitors 125 and130 can form a part of the reactive circuit constituted overall by thereactances comprised between the converter 135 and the charging device105.

As already mentioned, this reactive circuit is set up in such a way thatthe electric power (e.g., tension and/or current) applied to the activeswitch 155, and preferably also its derivative in time, have a value ofsubstantially nil, during each step of transition of the active switch155 from off to on and from on to off.

This set-up essentially consists of a suitable choice of the reactivecomponents.

In other embodiments, such as the one illustrated in FIG. 4, thereactive circuit 145 can include two reactive grids, of which a firstreactive grid 175 for ensuring the proper functioning of the activeswitch 155, and a subsequent reactive grid 180, for ensuring a correctset-up of the system with a different charge from the one used totransmit the desired power.

The reactive circuit 145 normally also serves as a passband filter forthe tension wave that is transferred between the primary circuit 115 andthe secondary circuit 120. The band of frequencies allowed to pass fromthe filter also depends on the set-up of the reactive circuit 145.

In this regard, it is preferable for the reactive circuit 145 to be setup so as to pass one or more of the fundamental frequencies of thetension wave.

Considering the specific example in which the active switch 155 ispiloted by an electric signal square wave having a duty-cycle of 50%,the fundamental frequencies of the tension wave are those in odd order:the first, third, the fifth and so on. The reactive circuit 145 cantherefore be set up so as to let the first fundamental frequency of theelectric tension pass, in which case the converter 135 is in factassimilable to an e-class amplifier. Alternatively, the reactive circuit145 can be set up so as to let the third fundamental frequency of theelectric tension pass, or other odd harmonics, in which case theconverter 135 is in fact similar to an f-class amplifier. It is alsopossible for the reactive circuit 145 to be set up so as to let thefundamental frequencies of a higher order pass, or to let morefundamental frequencies pass simultaneously, in such a way as to realizean e/f class amplifier or the like.

As previously mentioned, during the switching on and off cycles of theactive switch 155, the inductor 150 undergoes continuous cycles ofcharging and discharging.

In this regard, it is preferable to size the inductor 150 so as to makeit fully discharge at each cycle. In other words, contrary to whathappens in a classically-dimensioned choke inductor, in which thecurrent passing through it can be considered constant, for this specificcase it is possible to dimension the choke inductor 150 to oscillate thecurrent crossing it between a maximum value and nil (avoiding howeverthe inversions). In this way, the value of the inductor is drasticallyreduced. Having lower inductor values is important for this specificcase because: the overall dimensions and the ohmic losses can becontained to modest proportions, and inductors can be used that arerealized for example by inductors wrapped in air or another materialwith low losses in the core of the inductor itself.

A problem that can arise with an apparatus 100 such as the one describedabove consists in the regulation of electric power transmitted to thecharging device 105. This is the issue that limits the use of e- or f-or e/f-class amplifiers in variable charge and unknown situations apriori.

To make this type of adjustment, FIG. 5 illustrates an embodiment of theapparatus 100 which differs from that of FIG. 4 only in that, downstreamof the converter 135 and preferably downstream also of the isolationcapacitors 125 and 130, in parallel with the rectifier 140, an electricline has been inserted comprising a capacitor 185 in series with afurther active switch 190, for example a transistor (e.g. BJT, FET,MOSFET, MESFET, JFET, IGBT and others).

The active switch 190 can be connected to a driver 195 suitable forgenerating and applying a pilot signal to the pilot head of the activeswitch 190, preferably a PWM electric signal or the like.

When the pilot signal is ON, the active switch 190 turns on (i.e. goesinto saturation allowing passage on the line); instead, when the drivesignal is OFF, the active switch 190 turns off (or passes intoinhibition, preventing current flow on the line).

The capacitor 185 has a value that is sufficiently high to be considereda short circuit with respect to the charging device 105, when the activeswitch 190 is turned on.

In this way, when the active switch 190 is turned on, the electricalenergy transferred from the isolation capacitors 125 and 130 ispredominantly diverted onto the capacitor 185, while when it is off, thecharging device 105 absorbs all the energy.

The electric power transmitted to the charging device 105 is thereforeinversely proportional to the time in which the active switch 190 isturned on, for example to the duty-cycle of the PWM electrical pilotsignal. Therefore, by adjusting the ignition time of the active switch190, for example by adjusting the duty cycle of the PWM electrical pilotsignal, it is advantageously possible to adjust the electric powertransferred to the charging device 105.

For example, the driver 195 can include a control circuit (notillustrated), which is configured to adjust the duty cycle of the PWMpilot signal, so as to attain a predetermined value of a characteristicparameter of the electric power to be transferred to the charging device105.

The electrical parameter that is characteristic of the electric powercan be the electric power itself, or it can be the tension of the powersupply of the charge or possibly the supply current transmitted to thecharging device.

More particularly, the control circuit may be configured to perform afeedback control which comprises: measuring the electrical parametercharacteristic of the electric power transferred to the charging device,for example through one or more tension and/or current sensors appliedto the secondary circuit 120; calculating the difference between themeasurement of the electrical parameter characteristic of the electricpower and the predetermined reference value; and adjusting the dutycycle of the PWM electrical pilot signal, such as to minimize thedifference.

Note that this method for regulating power can be applied to all thecircuit diagrams shown in the drawings and other circuits of the sametype.

In addition or alternatively to this control mode, the electric powertransmitted to the charging device 105 can also be adjusted by acting onthe primary circuit 115, for example by suspending the generation of thepilot signal pulses of the active switch 155, in such a way as toinhibit one or more on and off cycles of the active switch 155.

During the inhibited cycles the inductor 150 is not powered and thesystem continues to oscillate in a damped free oscillating mode. Duringthe cycles carried out, the inductor 150 is instead supplied and thesystem oscillates in a forced oscillations mode.

In this way, by suitably adjusting the number and/or the “suspended”pulse frequencies, the electric power transferred to the charging device105 is effectively regulated.

For this purpose, the driver 160 may comprise a control circuit (notillustrated), which is configured to adjust the number and/or thefrequency of “suspended” electrical impulses of the pilot square wave,in order to follow a predetermined value of an electrical parametercharacteristic of the electric power to be transferred to the chargingdevice 105.

In this case too, the electrical parameter characteristic of theelectric power can be the electric power itself, or it can be the powersupply tension of the charging device or possibly the supply currenttransmitted to the charging device.

In greater detail, the control circuit may be configured to perform afeedback control which comprises: measuring the electrical parametercharacteristic of the electric power transferred to the charging device,for example via one or more tension and/or current sensors applied tothe secondary circuit 120 or to the primary circuit 115; calculating thedifference between the measurement of the electrical parametercharacteristic of the electric power and the predetermined referencevalue; and regulating the number and/or the frequency of the “suspended”electrical impulses of the square wave drive, such as to minimize thedifference.

This technique of adjustment of the power can also be applied to all thecircuit diagrams shown in the drawings as well as to other circuits ofthe same type.

In addition or alternatively to the methods mentioned above, the powertransmitted to the charging device 105 can also be adjusted byregulating the direct electric tension generated by the source 110.

As shown in FIG. 2, the apparatus 100 may in fact comprise a DC/DCconverter 200, such as a linear converter, a switching converter, or anyother type, which is placed downstream of the source 110 and upstream ofthe switching circuit 142, for example upstream of the choke inductor150 (with reference to the diagrams of FIGS. 3 to 5).

The DC/DC converter 200 can be configured to provide a tension value atoutput that is different to the value of the input tension, and thusconsequently modifying the electric power transmitted to the chargingdevice 105.

As in the previous cases, the DC/DC converter 200 can also include acontrol circuit (not shown) suitable for adjusting the tension accordingto a desired value of an electrical parameter characteristic of theelectric power to be transferred to the electrical load 105, for exampleby means of a feedback control routine.

In this case too the electrical parameter characteristic of the electricpower can be the electric power itself, or it can be the power supplytension of the charging device or possibly the supply currenttransmitted to the charging device.

Although this solution has been described with reference to the genericcircuit of FIG. 2, it is obvious that the same may apply to all thecircuit diagrams shown in the drawings as well as to others of the sametype.

As illustrated in FIG. 6, in an embodiment of the invention each versionof the apparatus 100 described above can be realized as a converterdevice 250 (meaning a single component), which can be connected viacables to the electrical charging device 105.

In this case, all the essential components of the apparatus 100,including in particular the converter 135, the isolation capacitors 125and 130, the rectifier 140, any filter and tension stabilization stagesand the rectifier 111 if present, can be integrated into a single“indivisible object” which can be connected on one side with the sourceof alternating tension 112, or with the DC tension source 110, and onthe opposite side with the charging device 105.

In particular, each of the isolation capacitors 125 and 130 can berealized in the usual way as a pre-assembled capacitor, which isinstalled as a single unit in the “indivisible object”.

Even the charging device 105 may be part of that “indivisible object.”

Alternatively, in a very important alternative embodiment of theinvention, any version of the apparatus 100 described above can berealized as a system for wireless transmission of power between twoseparate devices, without galvanic connection between them.

As shown in FIG. 7, said wireless transmission system thus comprises apower supply device 300 and a user device 305, separate and independentfrom the power supply device 300, i.e. not exhibiting any type ofphysical/mechanical connection with the power supply 300.

The user device 305 may be any electrical/electronic device, such as amobile phone, a computer, tablet, lighting system, television set orother, provided with its own external body or casing 310 independent ofthe external body or casing 315 of the supply device 300.

The power supply device 300 can comprise the components of the apparatus100 that define the primary circuit 115, including in particular theconverter 135 and the rectifier 111 if present, which can be integratedinto a single “indivisible object” suitable for connecting via cablewith the source of alternating tension 112, or possibly with the DCtension source 110.

The user device 305 can instead include the components of the apparatus100 that define the secondary circuit 120, including in particular therectifier 140 and the charging device 105, which can be represented bythe internal batteries to be recharged and/or electronic devices to besupplied to enable the user device 305 to operate.

The isolation capacitors 125 and 130 may be defined by a pair ofarmatures 320 incorporated in the power supply device 300, and byanother pair of armatures 325 incorporated in the user device 305.

Each armature 320 and 325 may be realized by any layer of conductivematerial 340 coated with a layer of dielectric material 345.

The armatures 320 and 325 must be placed in the respective devices sothat by nearing the user device 305 to the power supply device 300, forexample by placing the former on the latter, the conductor layer 340 ofeach armature 320 realizes, with the conductor layer 340 of acorresponding armature 325, and with the dielectric material 345 whichremains interposed between them, respectively the isolation capacitor125 or the isolation capacitor 130.

In this regard, the outer casing 315 of the supply device 300 maycomprise a support wall 330, and the outer casing 310 of the user devicemay comprise a reference wall 335, which will be facing and supported onthe wall of the support 330 of the feeder device 300.

The armatures 320 can be applied on the external or internal surface ofthe support wall 330, while the armatures 325 may be applied on theexternal or internal surface of the wall 335.

As shown in FIG. 8, each armature 320 and 325 may more preciselycomprise three superposed layers, in which the conductive layer 340 isinterposed between the upper dielectric layer 345 and a lower dielectriclayer 350. The lower dielectric layer 350 can be supported on asubstrate 355.

The upper dielectric layer 345 of each armature 320 is destined to gointo direct contact with the upper layer of an armature 325.

The substrate 355 of each armature 320 can be a portion of thesupporting wall 330 of the supply device 300, while the substrate 355 ofeach armature 325 may be a portion of the reference wall 335 of the userdevice 305.

The substrate 355 may be made of any conductive or dielectric material,provided it is sufficiently distant from the conductive layer 340. If,however, is very close to the conductive layer 340, it is better for thesubstrate 355 to be a dielectric characterized by low leakage and lowdielectric constant when stressed by the electric field which variesover time. If the substrate 355 is a dielectric material, the lowerdielectric layer 350 could be absent.

The lower dielectric layer 350, if present, is preferably characterizedby low leakage and low relative dielectric constant, so that theelectric field propagates little in the direction of the substrate.

The conductive layer 340 can be of any electrically conductive orsemiconductive material, possibly doped, although the best results areobtained with low resistivity materials.

The upper dielectric layer 345 should preferably enable the bestpossible electrical coupling between the conductive layers 320 of thearmatures 320 and the armatures 325. Therefore, the upper dielectriclayer 345 is preferably as thin as possible, characterized by lowleakages and a high relative dielectric constant.

In this way, the electrical charging device 105 of the user device 305may be powered or recharged, without any galvanic connection, simply byplacing the plates 325 of the user device 305 on the armatures 320 ofthe feeder device 300, such that the conductive layers 340 and the upperdielectric layers 345 of the armatures 320 and 325 realize the first andthe second isolation capacitors 125 and 130 of the apparatus 100,enabling the transferring of power to the charging device 105.

With the proposed layout, by virtue of using a high frequency resonantconverter 135 (e.g. class “e”, “f” or “elf”), or resonant with higherharmonics than the pilot, allowing high power frequencies of thearmatures 320 and 325, armatures 320 and 325 of very small dimensionsare possible, such as to be easily housed internally of electronicdevices in common use such as cell-phones, computers, cameras, MP3players, lighting systems, for example LED systems, television sets andmore besides.

At the same time, it can be guaranteed that the tension attained by thearmatures 320 and 325 is extremely low (for example a few tens ofvolts), which avoids any risk to the user even in the absence of thecontrol circuits.

In this way very high energy efficiency is ensured, as well as a drasticreduction in overall dimensions, low working tensions, high transmittedpower, and low production costs.

Naturally a technical expert in the sector might make numerousmodifications of a technical-applicational nature to what has beendescribed herein above, without forsaking the scope of the presentinvention, as claimed in the following.

REFERENCES

-   -   100 apparatus    -   105 electrical load    -   110 source of direct tension    -   111 rectifier    -   112 source of alternating current    -   115 primary circuit    -   120 secondary circuit    -   125 first capacitor    -   130 second capacitor    -   135 converter    -   140 rectifier    -   142 switching circuit    -   145 reactive circuit    -   150 inductor    -   155 active switch    -   160 driver    -   165 capacitor    -   170 inductor    -   175 first reactive grid    -   180 second reactive grid    -   185 capacitor    -   190 active switch    -   195 driver    -   200 DC/DC converter    -   250 converter device    -   300 supply device    -   305 user device    -   310 external casing    -   315 external casing    -   320 armature    -   325 armature    -   330 support wall    -   335 reference wall    -   340 conductor layer    -   345 upper dielectric layer    -   350 lower dielectric layer    -   355 substrate

1. A method for transferring electric power to an electrical load (105),comprising steps of: converting an direct electric current into anelectric tension wave, applying the electric tension wave in inlet to atleast a couple of electric capacitors (125, 130) including a firstcapacitor (125) and a second capacitor (130), supplying the electricalload (105) with the electric tension in outlet from the capacitors (125,130).
 2. The method of claim 1, comprising a further step of: rectifyingthe electric tension wave in outlet from the electrical capacitors(125,130).
 3. The method of claim 1, wherein the conversion stepcomprises: alternatingly switching an active switch (155) on and off. 4.The method of claim 3, wherein the conversion step comprises: loweringthe electrical power dissipated by the active switch (155) to asubstantially nil value during each transition step of the active switch(155).
 5. The method of claim 1, comprising steps of: preventing one ormore switching on and off cycles of the active switch (155).
 6. Themethod of claim 5, wherein a regulating of the electrical powertransferred is performed with a feedback control which comprises thesteps of: measuring the electrical power transferred to the chargingdevice, calculating the difference between the electrical power measuredand the predetermined reference value, and regulating the number and/orthe frequency of the switching on and off cycles inhibited, such as tominimize the difference.
 7. The method of claim 1, comprising steps of:temporarily deviating the electric tension wave onto an electrical lineset in parallel to the electrical load (105), wherein the electric linecomprises a second active switch (190) and a third capacitor (185)connected in series with the second active switch and having a capacitorvalue that is sufficiently high to be considered a short-circuit withrespect to the charging device, when the second active switch isswitched on.
 8. The method of claim 7, wherein a regulating of theelectrical power transferred is performed with a feedback controlcomprising the steps of: measuring the electrical power transferred tothe charging device, calculating the difference between the measuredelectrical power and the predetermined reference value, and regulatingthe duration of the deviation step and/or the frequency with which thedeviation step is eventually repeated, such as to minimize thedifference.
 9. The method of claim 1, comprising a step of: regulatingthe direct electric tension.
 10. The method of claim 1, wherein thedirect electric tension is obtained via a step of rectifying analternating electric current.
 11. The method of claim 1, wherein thefirst armature (325) of each of the electrical capacitors (125, 130) isinstalled on a user device (305), while the second armature (320) ofeach of the electrical capacitors (125, 130) is installed on a supplydevice (300) separate and independent of the user device (305), andwherein the method comprises nearing the user device (305) to the supplydevice (300) such that the armatures (320, 325) installed on eachthereof realize the capacitors (125, 130).
 12. An apparatus (100) fortransferring electric power to an electrical load (105), comprising: atleast a pair of electrical capacitors (125, 130) including a firstcapacitor (125) and a second capacitor (130), means (135) for convertinga direct electric tension into an electric tension wave, means forapplying the electric tension wave in inlet to the capacitors (125,130), means for supplying the electrical load (105) with the electrictension in outlet from the capacitors.
 13. The apparatus of claim 12,comprising: means (140) for rectifying the electric tension wave inoutlet from the capacitors (125, 130).
 14. The apparatus (100) of claim12, wherein the converter means (135) comprise a switching circuitprovided at least with: an active switch (155), means (160) forgenerating an electrical pilot signal suitable for switching the activeswitch (155) on and off.
 15. The apparatus (100) of claim 14, whereinthe converter means (135) comprise a reactive circuit (145) set up suchas to lower the electrical power dissipated by the active switch (155)to a substantially nil value, during each transition step of the activeswitch (155).
 16. An apparatus (100) according to claim 15, wherein theconverter means (135) comprise: a first inductor (150) connected inseries with a DC tension source 110 and with the active switch (155),said active switch (155) having a head connected with the outputterminal of the inductor (150), and the other end connected in shortcircuit with the source (110), and the piloting head connected with adriver (160), a further capacitor (165) connected in series with thefirst inductor (150) and in parallel with the active switch (155), theoutput terminal of said further capacitor (165) being connected in shortcircuit with the tension source (110), via an electrical branch to whicha head of the active switch (155) and the second isolation capacitor(130) are also connected.
 17. The apparatus (100) of claim 16, whereinthe converter means (135) comprise a second inductor (170) connected inseries with both the first inductor (150) and the first isolationcapacitor (125), and connected in parallel with both the active switch(155) and the third capacitor (165).
 18. The apparatus (100) of claim15, wherein the reactive circuit (145) is configured as a passbandfilter for the tension wave, and is set up so as to pass one or more ofthe fundamental frequencies of the tension wave chosen among the groupconstituted by: the first fundamental frequency of the electric tension,the third fundamental frequency of the electric tension, or other oddharmonics of a higher order.
 19. The apparatus (100) of claim 14,comprising means (160) for controlling the electrical pilot signal, thecontrol means being configured for: suspending the generating of theelectrical pilot signal, such as to prevent one or more consecutiveswitching on and off cycles of the active switch (155).
 20. Theapparatus of claim 19, wherein the control means are configured such as:measuring, using appropriate sensors, an electric parametercharacteristic of the electric power transferred to the load (105),calculating the difference between the measurement of the electricalparameter characteristic of the electric power and the predeterminedreference value, and regulating the number and/or the frequency ofswitching-on and off cycles which are inhibited, such as to minimize thedifference.
 21. The apparatus (100) of claim 14, comprising: means (185,190) for temporarily deviating the electric tension wave onto anelectrical line set in parallel to the electrical charging device (105)wherein the means for deviating the electric tension wave comprise asecond active switch (190), a third electric capacitor (185) arranged inseries to the second active switch (190) along the electric line, andmeans for generating an electrical pilot signal for switching on and offthe second active switch (190) alternatingly, the third electriccapacitor (185) having a sufficiently high value to be considered as ashort circuit with respect to the load (105), when the second activeswitch is on.
 22. The apparatus of claim 21, comprising a controlcircuit configured for: measuring an electric parameter characteristicof the electric power transferred to the load (105), calculating thedifference between the measurement of the electric parametercharacteristic of the electric power and the predetermined referencevalue, and regulating the duty-cycle of the electric pilot signal of thesecond active switch, such as to minimize the difference.
 23. Theapparatus (100) of claim 12, comprising: means (200) for regulating thedirect electric tension.
 24. The apparatus (100) of claim 12,comprising: means (111) for rectifying an alternating electrical currentin order to obtain the direct electric tension.
 25. The apparatus (100)of claim 12, wherein each of the capacitors (125, 130) is apre-assembled component, and wherein the capacitors (125, 130) areinstalled in a same device (250).
 26. The apparatus (100) of claim 12,comprising a user device (305) and a supply device (300) separate andindependent of the user device (305), wherein the user device (305)comprises a first armature (320) of each of the capacitors (125, 130),while the supply device (300) comprises the second armature (320) ofeach of the capacitors (125, 130).